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Updated: Jan 2, 2026
Engineering Oncogenic Heterozygous Gain-of-Function Mutations in Human Hematopoietic Stem and Progenitor Cells
Published on: March 10, 2023
The Expression of Myeloproliferative Neoplasm-Associated Calreticulin Variants Depends on the Functionality of
Olivier Mansier1,2,3, Valérie Prouzet-Mauléon1, Gwénaële Jégou4
1INSERM U1218, ACTION, Université de Bordeaux, UFR Sciences de la Vie et de la Santé, 33000 Bordeaux, France.
Background:
Mutations in CALR observed in myeloproliferative neoplasms (MPN) were recently shown to be pathogenic via their interaction with MPL and the subsequent activation of the Janus Kinase - Signal Transducer and Activator of Transcription (JAK-STAT) pathway. However, little is known on the impact of those variant CALR proteins on endoplasmic reticulum (ER) homeostasis.
Methods:
The impact of the expression of Wild Type (WT) or mutant CALR on ER homeostasis was assessed by quantifying the expression level of Unfolded Protein Response (UPR) target genes, splicing of X-box Binding Protein 1 (XBP1), and the expression level of endogenous lectins. Pharmacological and molecular (siRNA) screens were used to identify mechanisms involved in CALR mutant proteins degradation. Coimmunoprecipitations were performed to define more precisely actors involved in CALR proteins disposal.
Results:
We showed that the expression of CALR mutants alters neither ER homeostasis nor the sensitivity of hematopoietic cells towards ER stress-induced apoptosis. In contrast, the expression of CALR variants is generally low because of a combination of secretion and protein degradation mechanisms mostly mediated through the ER-Associated Degradation (ERAD)-proteasome pathway. Moreover, we identified a specific ERAD network involved in the degradation of CALR variants.
Conclusions:
We propose that this ERAD network could be considered as a potential therapeutic target for selectively inhibiting CALR mutant-dependent proliferation associated with MPN, and therefore attenuate the associated pathogenic outcomes.
Insights
Calpastatin (CALR) mutations in myeloproliferative neoplasms (MPN) do not affect endoplasmic reticulum (ER) homeostasis. However, CALR variants are degraded via ER-associated degradation (ERAD), presenting a potential therapeutic target for MPN.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Calpastatin (CALR) mutations are pathogenic in myeloproliferative neoplasms (MPN) by activating the JAK-STAT pathway.
- The effect of CALR mutations on endoplasmic reticulum (ER) homeostasis remains largely unknown.
Purpose of the Study:
- To investigate the impact of wild-type (WT) and mutant CALR expression on ER homeostasis.
- To identify mechanisms responsible for CALR mutant protein degradation.
Main Methods:
- Assessed ER homeostasis by quantifying Unfolded Protein Response (UPR) target genes and XBP1 splicing.
- Utilized pharmacological and siRNA screens to identify CALR degradation pathways.
- Performed coimmunoprecipitation to define CALR disposal actors.
Main Results:
- CALR mutants did not alter ER homeostasis or hematopoietic cell sensitivity to ER stress-induced apoptosis.
- CALR variant expression is low due to secretion and ER-Associated Degradation (ERAD)-proteasome pathway degradation.
- A specific ERAD network involved in CALR variant degradation was identified.
Conclusions:
- The identified ERAD network is a potential therapeutic target for MPN.
- Inhibiting this network could selectively target CALR mutant-dependent proliferation.
- This approach may attenuate pathogenic outcomes associated with MPN.
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